Low-tension fluid-heating apparatus



Fe? M, E93@ R. A. CARLETQN LOW TENSION FLUID HEATNG APPARATUS Filed July12, 1927 4; Sheets-Sheet l 4 if, T.. WW

NVENTOR. Rohm .-Co1ireon ATTORNEYS.

Feb. 11, 1930. R. A. cARLEToN LOW TENSION FLUID HEATING APPARATUS 'FiledJuly 12I 1927 4 Sheets-Sheet 2 m .5. m -wmm V m. T NVC. Am A im@ 7 5Peb. ll, 1930. R. A. CARLETON 1,746,522

LOW TENSION. FLUID HEATING APPARATUS Filed July l2, 1927 4 Sheets-Sheet3 Pk/ENTER: Rober A CGrleTon :EJLll-WMJff l #YT-rn RN 1.15

Feb. l1, 1930. R. A. CARLETON LOW TENSION FLUID HEATING APPARATUS 1927 4Sheets-Sheet 4 Filed July l2 L UUHHUHHHHH n 1 l l l i I l Patented Fei.11, 1930 UNITED STATES PATENT OFFICE LOW-TENSION FLUID-HEATING APPARATUSApplication led July 12,

This invention relates to `improvements in lluid heating apparatus andthe general object of the invention is to provide a simple and ruggedapparatus, of low cost of construction, and of high eii'iciency, and inwhich practically no substantial deterioration of the heating elementswill be produced by usage.

A further object of the invention is to provide an apparatus of thischaracter in which radiation losses will be reduced to a minimum and noheat insulation required.

A further object of the invention is to provide an electric Huid heatingapparatus of this character in which the heating element-s will presenta maximum surface area and in which the fluid will be directly heated bycontact with the large surfaces of the heating element, therebypermitting a rapid transfer of heat from the heating element to thefluid being heated, so that the same can be operated at a comparativelylow temperature, or at a temperature slightly above that of the fluidbeing heated, thus avoiding pitting or deposits upon the surface of theheating element and decomposition or other chemical or mechanicalchanges in the fluid which otherwise would be effected by excessivetemperatures.

A further object of the invention is to provide an electric heater inwhich the heating elements are heated by an electric current of loWpotential.

A further object of the invention is to provide a heating apparatus inwhich the low ments by a step-down transformer and is insulated from theusual lighting or power systems which supply current to the primarycircuit of the transformer in which, under the usual practice, one sideot the service is grounded, thereby avoiding dangerous voltages in theheating apparatus.

A further important object of the invention is to provide an electricheating apparatus of the character specified in which narrowly spacedheat-ing elements are immersed in the fluid to be heated and the currentsupplied to said heating elements is caused to pass through alternatingheating elements in optension current is supplied to the heating ele-1927. Serial Fo. 205,135.

posite directionss thereby substantially avoiding the effects ofself-induction.

A further object ot the invention is to provide means for controllingthe supply of the electric current to the heating elements so as tomaintain a uniform maximum temperature of the fluid within, or deliveredfrom, the apparatus.

A further object of the invention is to provide means operable by theflow of fluid supplied to the apparatus to control the current suppliedto the apparatus and whereby cessation of flow of the fluid into theapparatus will interrupt the supply of the current to the heatingelements.

A further object of the invention is to provide an electric heatingapparatus of this character in which the heating 'elements may operatewith a direct current or a single phase or a polyphase alternatingcurrent at any desired voltage or frequency depending upon the characterof the material of the heating elements and the character of the fluidbeing treated. For example, the heating of Water and light liquids mayrequire the use of a current of one hundred or more volts7 While withbrine, strongly acid liquids, or the like, a low tension current ot twoor more volts might be required.

The present invention contemplates the provision of an electric heatingapparatus in which Va heating element, 0r plurality of elementspresenting large surfaces are immersed and directly exposed to the fluidbeing heated and are supplied with a relatively low tension current ot'suilicient amperage to raise the heating elements to the desiredtemperature.

By the use of such relatively low tension currents leakage of thecurrent through the fluid being heated is reduced to a minimum. Bypassing a current in opposite directions to alternating heating units,self-induction is Wholly or substantially avoided.

Desirably the fluid is caused to flow in a predetermined directionbetween narrowly spaced heating elements so that it is heated mainly bydirect contact with the heating elements. Preferably the heatingelements are of spiral form and the Huid is caused to How through thenarrow spaces between the adjacent heating elements toward the centerthereof and is delivered from a central outlet. rIhis constructionpermits the elements to present a maximum heating surface. Radiationlosses are prevented for the reason that the cold fluid enters betweenthe peripheral edges of the heating elements and after being heated isdischarged through the central outlet so that the heating elements as awhole are surrounded by a body of cool fluid which does notradiate heatto any substantial degree through the wall of the receptacle, therebyavoiding the necessity `of external heat insulation. y

The present invention is adapted in itsv ap'- plication to variouspurposes, including the heating of aquiescent body of fluid,instantaneous heating of a flowing fluid such as water` the generationof steam, the superheating of steam, vaporizing volatile materials,-

evaporating liquids, concentrating liquids, as well as other uses.

Illustrative embodiments of the invention are disclosed in theaccompanying drawings', 1n which, v

Fig. 1 is a vertical sectional view of apreferred form of apparatus forheating the flowing liquid or gaseous fluid;

Fig. 2 is a detail sectional view on line 2-2 Fig. 1, having in commonwith Fig. 1 an illustration of a single phase step-down transformer Fig.3 isa vertical sectional view of a modified formof apparatus showing themanner in which a polyphase current may be supplied to the heatingelements;

Fig. 4 is a horizontal sectional view on line 4-4 Fig. 3;

5 is a vertical sectional view of a slightly modified form of theapparatus particularly adapted for steam generation;

Fig. 6 is a horizontal sectional view on line 6-6 Fig. 5;

Fig. 7' is a vertical longitudinal sectional view of a form of apparatusparticularly a cylindrical wall 1 of steel or other material adapted towithstand pressure under which the fluid is being treated, and also toresist corrosion. or chemical action by the chemicals contained in thefluid. The lower end of the cylindrical wall is connected by a flange 2,or other water-tight connection, with a head 3 of suitable materialhaving a central boss pass in the op head above the fitting 7, isprovided with an outlet pipe 12 through which the fluid may bedischarged from thetank or receptacle.

Fluid may be aitroduced into the lower portion of the receptacle in anysuitable manner. In the construction illustrated, however, the tubularmember 6 is provided near its lower end with a web or closure 13 and theportion of the tubular member below said closure is provided with aseries of ports 14 through which fluid introduced at the lower end ofthe tubular member is discharged into the lower portion of thereceptacle. The tubular member 6 is provided above the closure 13 with aseries of ports 15 which permit the fluid to flow from the receptacleinto the chamber of the tubular member and thence through the outlet 12.

The heating elements comprise preferably a plurality of curved thinplates of relatively high resistance material, such as monel metal whichis non-corrodible and generally resistant to chemical action. In thepreferred construction the heating elements are in the form of twonarrowly separated spiral plates 16l and 17 which are 'connected attheir inner ends to diametrically opposite portions of the wall of thecentral tubular member 6. The outer ends of these spiral plates areconnected to suitable terminals of an electric circuit so that thecurrent will flow, for example, through the spiral plate 16 to thecentral tubular member 6, and from the central tubular member willposite direction through the spiral 17. By reason of this arrangementthe magnetic field caused by the flow of current in one plate isneutralized by the magnetic field caused b v the flow of current in theother plate, thus substantially preventing the effect of self-inductionand permitting the circuitl 21 and 22 which receive the lower ends ofthe spiral plates 16 and 17 respectively. The upper ends of the plates16 and 17 are seated in similar spiral grooves in an insulating d isk 23which is engaged by a spider 24 mounted upon the tubular member 6 andwhich may be clamped upon'the plates by a suitable nut 25.

Desirably the ends of the spider arms are connected by tension rods 26.By reason of this construction the spirally curved heating plates areheld firmly in position and at all times maintained in narrowly spacedrelation.

Any suitable means may be provided for supplying a suitable electriccurrent to the heating plates.

In the preferred construction illustrated herein the heating -current issupplied from the secondary 27 of an adjustable step-down transformer28. Low resistance conductors 29 and 30 lead from the secondary coil 27of the transformer to low resistance conductor bars 31 and 32 whichpreferably are connected to the'outer edges of the spiral plates 16 and17 throughout the length of the plates and are adapted to conduct acurrent of relatively low voltage of sufficient amperage to heat theplates 16 and 17 to the required temperature. A relatively high tensioncurrentis supplied through the conductors 33 and 34- and a manuallyoperable switch 35 to the primary 36 of the/transformer.

Desirably suitable means are provided for controlling the voltage of theprimary circuit of the transformer and also means desirably are providedfor breaking the circuit to the primary upon cessation of flow of uidthrough the tank or receptacle.

In the construction illustrated herein a thermostat 37, which may belocated within the receptacle, or preferably within the outlet pipe 12,in such a position that it is subject to the maximum temperature of thefluid, controls a high resistance branch or shunt, of the power circuit38, 39, embodying or having within it a solenoid 40, or other device,adapted automatically to operate a contact arm 41 to cut in or outcertain of the coils of the primary 36, thereby changing the voltage ofthe secondary and thus controlling the current delivered to the heatingelements.

Preferably hydraulic means are provided for interrupting the primarycircuit upon cessation of ilowof liquid through the apparatus. In theconstruction illustrated an inlet pipe 42. which communicates with thelower end of the tubular member 6, is provided with a pivotally mountedswitch 43 which is operated hydraulically by thefiuid flowing into thereceptacle to .complete a branch or shunt circuit 44 and 45 of the mainpower supplying circuit through a Contact breaking device 46 in theconductor 33 leading to the primary. This arrangement is such that whenwater is flowing through the inlet the branch circuit 44 and 45 iscompleted, thereby causing the closing of the contactor 46 to permit thecircuit to ow through theprimary.

Upon cessation of the low of Water through the inlet 42 to thereceptacle, the branch circuit 44 and 45 is broken and the contactoropened, thereby breaking the primary circuit and consequentlyde-energizing the transformer so that no current will iiow through theheating coils.

In the operation of the device the water entering into the lower portionof the tank or receptacle is caused by the imperforate lower head 20 toHow outwardly and upwardly along the cylindrical wall of the receptacle.The liquid then flows between the spirals of the heating plates 16 and17 to the center of the tubular member and enters ports therein and isfinally discharged through the outlet 12. By reason of this constructioncool fluid is always in Contact with the cylindrical wall 1 and theliquid is progressively heated, mainly by direct contact with both theinner and outer surfaces of the spirals throughout the greater part ofthe length thereof. As these spiral plates present large areas to arelatively small volume of iuid in the heater the fluid is very rapidlyheated and the heated fluid is discharged from the outlet at its maximumtemperature. By the employment of a low voltage current leakage of thecurrent through the fluid is reduced to a minimum. As the low tensionsecondary current is insulated from the high tension primary current,danger to the operator is avoided.

The apparatus thus described is of simple construction which may beproduced at a relatively low cost. It is automatic in operation. Itprovides a direct and rapid transfer of heat from the heating elementsto the fluid being heated. It permits the heating of the iuid by heatingunits presenting large surface areas. rllhe temperature can becontrolled at a small difference between that of the heating element andof the fluid and the close regulation of heat may be maintained at anytemperature. rIhe construction is of a. rugged nature and as the heatingelements are at all times immersed within the fluid they will not burnout. Inasmuch as cool Huid, which is introduced, is in contact with thewall of the receptacle or tank, no substantial radiation losses occurand no insulation is required. No deposit is formed upon them and nopitting of the heating elements occurs.

It will be obvious that apparatus embodying the 'invention may be madeof any size or capacity and of materials suitable for the use for whichthe apparatus is applied.,

In Figs. 3 and 4 a modified construction is illustrated which is adaptedfor a water circulation system. This construction comprises a preferablycylindrical tank or receptacle 47 having upper and lower water-tightheads 48 and 49 andl provided with an inlet pipe near the lower-endthereof and an outlet pipe 51 at its upper end, the pipes 50 and 51being adapted to be connected into a. Water storage tank or acirculating system.

In this construction a central, preferably tubular, member 52, having ascrew threaded lower end, is seated in a boss 53 in the lower head 48and is provided with spider arms 54 at a short distance above the head48. Strips 55 of insulating material are secured to the upper faces of.the spider arms 54 and are provided with grooves in which the loweredges of the yheating elements are mounted. The heating elements may beof any desired form, such as cylindrical or preferably spirally f"formed plates narrowly separated from each other and so arranged thatthe current will flow in opposite directions through alternating plates.

In the construction illustrated the heating elements comprise threespiral plates 56, 57 and 58, the central ends of vwhich are connectedpreferably at equal distances from each other to the central tubularmember 52.

The outer ends of the plates are connected respectively to conductorbars 59, 60 and 61 which are in turn connected to conductors 62, 63 and64 which pass through a block 65 of insulation in the wall of thereceptacle and are connected to the secondary 66 of athree-phasetransformer'to the primary 67 of which current is suppliedthrough the conductors 68, (39 and 70.

The resistance plates in this construction are so connected in thethree-phase circuit of the secondary that the magnetic field,

. caused by the current flowing in one direction in outer plates, isneutralized by the magnetic field caused by the return flow of currentin an intermediate plate; thus self-induction or induced voltage isgreatly reduced, thus permitting the circuit to operate at a high powerfactor. Y

A suitable thermostat 71, located in the upper portion of thereceptacle, and subject to the maximum heat of the fluid, may beemployed to control a branch 72, 73 of the primary circuit havingsuitable means, as heretofore described, for regulating the voltagesupplied to the secondary circuit of the transformer.

In Figs. 5 and 6 a modified form of apparatus is illustrated which isparticularly designed for a steam generator. This construction comprisesa preferably cylindrical boiler 74 having upper and lower heads 75 and76 with a supply pipe 77 leading through the lower head for introducingwater into the apparatus, and anoutletpipe 78 leadingfrom the upperhead. The boiler desirably is surrounded by heat insulation 79. Theheating elements in this construction, as in those previously described,comprise spiral plates 8O and 81 which are narrowly spaced apart withthe spirals alternating and both connected at their inner ends to acentral bar or tube 82 which is supported upon lower and upperside-shaped brackets 83 and 84 which are mounted upon suitablesupporting lugs 85 and 86 extending inwardly from the wall 74 of theboiler. Suitable strips of insulation 87 and 88, resting upon the upperand lower arms of the spider, are provided with grooves to receive theends of the spiral plates and 81 as above described. The boilerdesirably is provided with a usual glass water gauge 89 and other usualboiler equipment.

In addition to these the boiler, in this particular construction, isprovided with a pressure operated device 90 adapted to operate throughan electric circuit 91 and 92 to control a switch 93 in a circuit 94 and95 leading to a primary 96 of a step-down transformer. Conductors 97 and98 lead from the secondary 99 of the conductor to bars 100 and 101 whichare connected respectively throughout the edges of the high resistanceheating units 80 and 81. A water level is maintained at a suilicientheight to immerse the heating plates within the Water.

In the operation of this construction, when current is supplied to theprimary of the transformer, the electrically operated switch 93 will beclosed, thereby energizing the transformer and causing a low voltagecurrent to flow through the conductors 97 and 98 and the relatively highresistance heating elements or plates. rIhe heat generated in theheating plates or elements is transmitted directly to the water in whichthe plates are submerged. The heating of the water will cause it torise, thus causing an upward circulation of water between the plates anda downward circulation near the surrounding wall of the boiler. Thewater thus circulated will be rapidly raised to boiling temperature andthe steam will collect in the upper portion of the boiler and may bedelivered as rapidly as desired through the outlet pipe 78. When thesteam in the upper portion of the boiler has acquired the desiredpressure the pressure device 90 will operate to open the control switch93 in the circuit leading to the primary of the transformer, therebyde-energizing the transformer and cutting olf the secondary currentthrough the heating units. When the pressure of the steam in the boilerdrops below the desired amount, the pressure regulating device willagain close the switch 93, thus again energizing the transformer andcausing; another heating cycle. 4 i

It will be obvious that should it be desirable the control switch andthe transformer Vcan be so arranged that instead of disconform steamproduction at a desired pressure.

The principal advantages of this form of electric heater over othertypes of electric heaters now in use are low cost of manufacture;indestructibility; elimination of repairs or replacements; highefiiciency. due to comparatively large heating unit surfaces; the rapidtransfer of heat from the plates to the surrounding liquid which is indirect contact with the plates; operation at a much lower temperaturethan other types of heating elements because of the large heating area;avoidance of overheating by reason of `the constant contact of theliquid with the heating elements and the rapid circulation of the liquidby reason of the rapid transfer' of heat thereto.

This embodiment of the invention is particularly adapted for householdheaters of small size, such as for domestic steam or vapor` heating, butmay be constructed of sufciently large capacity for various indus trialuses.

A further embodiment of the which is particularly adapted superheating,is illustrated in Figs. 7 and 8. This construction may be substantiallylike that disclosed in Figs. 1 and 2 with the exception that thecylindrical wall 102 desirably is made of steel, cast iron, or othersuitable metal to withstand high temperatures and pressures, and isprovided with removinvention,

' able heads 103 and 104. The high resistance conductors 105 and 106desirably are of spiral form and are connected at their inner ends to acentral tubular member 107 having ports 108. The central tubular memberlikewise is provided with a closure 109 near the inlet end of thereceptacle with ports 110 in the wall of the tubular member to admitsteam into the cylindrical chamber formed by the wall 102 and heads 103and 104. The steam entering the chamber passes between the heatingplates 105 and 10-6 and through the port-s 108 into the chamber of thetubular member and is delivered through the outlet 111 in the mannerabove described.

In this construction conductors 112 and 113 lead from the secondary 114of a singlephase secondary of a transformer having a three-phase primaryto conductor bars 115 and 116 which are secured to the longitudinalouter edges of the spiral conductors. These spiral conductors 105 and106 are arranged in alternate relation and their inner edges are securedto the centraltubular member 107 as heretofore described.

In theI construction illustrated in Figs. 7 and 8 a thermostatic device117 controls a branch circuit 118- and V119 having therein a solenoid120, or other device for actuating a switch 121 to break the primarycircuit when the steam reaches a predetermined temperature. Obviouslythe pressure operated device for steam receptacle or drum between thenarrowly sep-` arated heating plates to the central tubular member fromwhich the superheated steam is discharged. In the operation of thisconstruction, as in those heretofore described, a rapid transfer of heatis maintained from the heating elements to the fluid which is circulatedbetween them so that the Huid is heated mainly by direct contact withthe heating elements. In this construction, as in those heretoforedescribed, the current passes through alternating plates in oppositedirections thereby neutralizing the effect of self-induction.

Obviously other means for regulating the current supplied to thetransformer, such as those heretofore described, or other usual types ofregulators, may be employed within the scope of the invention.

It will also 'be obvious that other types of heating units may be used,such for example, as a plurality of narrowly separated flat plates withmeans for passing the current through alternating plates in oppositedirections. Preferably, however, curved lplates are employed for thereason that greater surface areas may be presented thereby. Such curvedplates may be narrowly separated concentric cylindrical plates withmeans for passing the current through`alternating plates in oppositedirections. It has been found, however, that spiral plates of thecharacter herein described are the most desirable. The single spiralplate has been found to be very satisfactory where a direct current isemployed by reason of the large area it presents when coiled within areceptacle or boiler which.

electric power to the district in which the inl stallation is made.

It will be understood that the particular embodiments of the inventiondisclosed herein are of an illustrative character and not restrictive ofthe scope or meaning of the following claims.

Having thus described the invention, what is claimed as new, and desiredto be secured by Letters Patent, is:

- pass through to provide a continuous conductor, and meansl forconnectlng the other edges of sa1d plates' in an electric circuit tocause the current to said plates in opposite directions, whereby effectsof self-induction will be substantially neutralized.

'2. A fluid heating apparatus comprising a fluid-containing receptacle,a plurality of x heating elements of high electrical resistancepresent/ing large surface areas narrowly separated from one another andimmersed in said fluid, conducting means electrically connecting all ofsaid heating elements together at one end, means for supplying apolyphase current to the other ends -of said plates to cause the currentto pass through alternating plates in opposite directions, wherebyeffects of self-induction will be substantially neutralized.

3. A fluid heating apparatus comprising a fluid-containing receptacle, aplurality of thin metallic plates of high electrical resistancepresenting large surface areas narrowly separated from one another andimmersed in said fluid and in direct contact therewith, conducting meanselectrically connecting all of said plates together at one end, meansfor supplying a polyphase current to the free ends of said plates tocause the current to flow in opposite directions through alternatingplates, whereby effects of self-induction will be substantiallyneutralized.

4. A fluid heating apparatus comprising a fluid-containing receptacle, aplurality of thin metallic plates of high electrical resistancepresenting large surface areas narrowly separated from one another andimmersed in said fluid and in direct contact therewith, conducting meanselectrically connecting all of said plates together at one end, meansforsupplying a polyphase current to the free ends of said plates tocause the current to flow in opposite directions through alternatingplates, whereby effects of self-induction will be substantiallyneutralized, and means for causing the liquid to flow through in thesame general direction through all of the spaces between said plates.

5. A fluid heating apparatus comprising a fluid-containing receptacle, aplurality of narrowlyspa'ced heating elements immersed in said fluid',means for passing an electric current through alternating elements inopposite directions, whereby effects of self-induction will besubstantially neutralized, means for causing the fluid to flow in apredetermined` direction relatively to the surfaces of said elements andthermostatic means subject to directions, whereby effects ofself-induction will be substantaially neutralized, means for causing thefluid to flow in a predetermined direction relatively to the surfaces ofsaid elementsand means lautomatically operable by the flowl of fluidthrough said receptacle to cause the electric current to besupplied tosaid plates and to prevent the supply of said current. uponsubstantialcessation of said flow. y

7.' A fluid heating apparatus comprising a I fluid-containingreceptacle, a plurality of narrowly separated, thin, spirally curvedconducting plates of high electric resistance material presenting largesurface areas, means for passing an electric current through alternatingplates in opposite directions and means for causing the fluid to flowbetween said plates in the direction of the spiral.

8. A fluid heating apparatus comprising a fluid-containing receptacle, aplurality of narrowly spaced curved metallic plates of high electricresistance material presenting large substantially parallel vsurfaceareas extending longitudinally of said receptacle and in direct Contactwith the fluid therein, means for introducing fluid into the lowerportion of said receptacle, means for delivering the fluid from theupper portion of said receptacle and means for passing an electriccurrent through alternating plates in opposite directions. A9. Afluidheating apparatus comprising a fluid-containing receptacle having afluid inlet at one end and an outlet at the other end and a heating unitimmersed in said fluid comprising a metallic plate of high resistancematerial of concentric spiral form arranged axially of said receptacleand presenting a large surface area, means for causing the fluid to flowfrom the periphery of said spiral toward the axis thereof in directcontact with said plate and means for passing an electric currentthrough said plate.

10. A fluid heating apparatus comprising a cylindrical fluid-containingreceptacle having a fluid inlet at one end and an outlet at the otherend and a heating unit immersed in said fluid of concentric spiral formar-` ranged axially of said receptacle and presenting a large surfacearea in direct contact with the fluid and with the spirals thereofnarrowly spaced apart and means for passing an electric current through`said heating unit.

11. A fluid heating apparatus comprising a fluid-containing receptaclehaving a fluid inlet at one end thereof and a central tubular outletextending axially of said cylinder and provided with ports, a heatingunit immersed in said fluid comprising a plate of high resistancematerial of concentric spiral form extending outwardly from said tubularoutlet and presenting a large surface area, imperforate heads ofinsulating material engaging the ends of said plate and operable tocause the Huid to flow from the peripheral edge of said plate toward theports of said tubular outlet andy means for passing an electric currentthrough said plate.

12. A uid heating apparatus comprising a cylindrical fluid-containingreceptacle having a fluid inlet at one end thereof and a central tubularoutlet extending axially of said cylinder and provided with ports, aheating unit of con-centric spiral form immersed in said fluid andextending outwardly from said tubular outlet and presenting a largesurface area in direct contact with the iuid, imperforate heads ofinsulating material engaging the ends of said heating unit and operableto cause the fluid to flow from the peripheral edge of said unit towardthe ports of said tubular outlet, and means for passing an electriccurrent through said unit.

13. A fiuid heating apparatus comprising a fluid-containing receptaclehaving a fluid inlet at the lower portion thereof and a central tubularoutlet having a closure at the lower portion thereof above said inletand having ports in its wall above said closure, a plurality of narrowlyspaced concentric spiral metallic plates of high resistance materialimmersed in said fluid and presenting large surface areas extendingoutwardly from said tubular outlet, imperforate heads of insulatingmaterial engaging the ends of said plate operable to cause the fluid toflow from the peripheral edges of said plates toward the ports of saidtubular outlet and imeans for passing an electric current through saidplates.

14. A fiuid heating apparatus comprising a fluid-containing receptaclehaving a fiuid inlet at the lower portion thereof and a central tubularoutlet having a closure at the lower portion thereof above said inletand having ports in its wall above said closure, a plurality of narrowlyspaced concentric spiral heating elements presenting large surface areasextending outwardly from said tubular outlet, imperforate heads ofinsulating material engaging the ends of said heating elements operableto cause the fluid to fiow from the peripheral edges of said heatingelements toward the ports of said tubular outlet, and means for passingan electric current through said heating elements.

15. A fluid heating apparatus comprising a fluid-containing receptaclehaving a fluid inlet at the lower portion thereof and a centrel tubularoutlet having a closure at the lower portion thereof above said inletand having ports in its wall above said closure, a plurality of narrowlyspaced spiral plates of high resistance material presenting largesurface areas extending outwardly from said tubular outlet, imperforateheads of insulating material engaging the ends of said plate operable tocause the Huid to flow from the peripheral edges of said plates towardsaid tubular outlet and means for passing an electric current throughalternating plates in opposite directions, whereby edects ofselfinduction will be substantially neutralized.

16. A Huid heating apparatus comprising a cylindrical fluid-containingreceptacle, a tubular member extending centrally therethrough having inits wall inlet ports communicating with the lower portion of saidreceptacle, a closure above said inlet ports and a plurality of seriesof other ports above said closure, a plurality of narrowly spaced thinplates of high resistance material presenting large surface areasextending outwardly from said tubular member, an imperforate head ofinsulating material mounted upon said tubular member above and inproximity to said closure, engaging the lower ends of said plates and asimilar head engaging .the upper ends of said plates operable to causethe fluid to fiow from the peripheral edges of said plates toward saidItubular member and means'for passing an electric current of lowpotential through alternating plates in opposite directions, wherebyeffects of selfinduction will be substantially neutralized.

17. A fluid heating apparatus comprising a fluid-containing receptacle,a plurality of narrowly spaced heating elements immersed in said fluid,means for passing an electric current of relatively low voltage throughsaid heating elements including a step-down transformer having terminalsof its secondary circuit connected respectively to alternating heatingelements to cause the current to flow through said alternating plates inopposite directions, means for supplying a current of relatively highvoltage to the primary of said transformer, a thermostat subject tosubstantially the maximum temperature within the receptacle and meansoperable by said thermostat for controlling the current supplied to theprimary of said transformer.

18. A fluid heating apparatus comprising a fluid-containing receptaclehaving an inlet and an outlet, a plurality of narrowly spaced platesofhigh resistance material immersed in said fluid, means for passing anelectric current of relatively low voltage through said plates includinga step-down transformer having terminals of its secondary circuitconnected respectively to alternating plates to cause the current insaid plates to fiow through alternating plates in opposite directions,means for supplying a current of relatively high voltage to the primaryof said transformer, a thermostat Subject to the temperature of thefluid passing through the outlet of said receptacle and means operableby said thermostat for controlling the current supplied to the primarycircuit of said transformer.

19. A Huid heating apparatus comprising a fluid-containing receptaclehaving an inlet and an outlet, a plurality of narrowly spaced plates ofhigh resistance material immersed in said iuid, means for passing anelectric current of relatively 10W voltage through said plates includinga step-down transformer having terminals of its secondary circuitconnected respectively to alternating plates to cause the current insaid plates to flow through alternating plates in opposite directions,means for supplying a current of relatively high voltage to the primaryof said transformer, and means operable by the How of iiuid through saidinlet to control the current supplied to the primary circuit of saidtransformer.

20. A fluid heating apparatus comprising a fluid-containing receptaclehaving an inlet and an outlet, a plurality of narrowly spaced plates ofhigh resistance material immersed in said fluid, means for passing anelectric current of relatively low voltage through said platesincluding' a step-down transformer aving terminals of its secondarycircuit connected. respectively to alternating plates to cause Ithecurrent in said plates to flow through alternating plates in oppositedirections, means for supplying a current of relatively hightransformer, means operable by the flow of fluid through said inlet tocontrol the current supplied to the primary circuit of said transformer,a thermostat subject to substantially the maximum temperature of theiuid in said receptacle and means operable by said thermostat forcontrolling the current supplied to the primary circuit of saidtransformer.A

In testimony whereof, I have signed my name to this s ecifiaction.

R BERT A. CARLETON.

voltage to the primary of said e

